Project Summary/Abstract Autoimmune diseases like type 1 diabetes arise through a breakdown in immune tolerance. We have now come to understand that immune tolerance consists of a multi-layered network that keeps such untoward responses in check. In this program project grant, three complementary teams will be working together to further unravel how these checkpoints operate to improve our understanding of autoimmunity and ultimately improve its treatment. This program project will have three highly collaborative and interactive projects headed by Drs. Mark Anderson (Project 1), Jeff Bluestone (Project 2) and John Kappler (Project 3) along with two scientific cores (Animal core and Molecular core). The major themes of the grant are: 1. The impact of central thymic tolerance on the T effector and Treg repertoire in T1D.. 2. Insulin as a critical self-antigen specificity for both T effectors and T regulatory cells in T1D. 3. Peptide specificity of Tregulatory cells in T1D 4. Using peptide binding characteristics of islet antigens to improve bioassays and tolerance methods. The long term objectives of this work is to improve our understanding of how T cell tolerance is controlled and the further refining the specificity of the autoreactive T cell response in type 1 diabetes. The investigators will be using state of the art tools in both animal models and in human subjects with type 1 diabetes. Results of these studies will help further refine our understanding of autoimmunity and help improve methods for its treatment and diagnosis.